The present invention relates to a plasma monitoring method, a plasma processing method, a method of manufacturing a semiconductor device, and a plasma processing system by which it is possible to detect specified radicals with high accuracy.
In the development of ULSI devices in recent years, a variety of investigations have been made by companies, with realization of higher operating speeds and lower power consumptions kept in mind. In these circumstances, the multi-layer wiring technology using low-dielectric-constant material films (the so-called low-k films) and copper (Cu) has come into general use, and securing a high wiring reliability has come to be a very important problem.
For example, in the process of using an SiOCH-based low-dielectric-constant material to form an inter-layer insulation film, as shown in FIG. 6A, an SiOCH-based film 102 and an SiO2 film 103 sequentially formed on a substrate 101 are provided with a groove 105 by etching by using a mask composed of a resist 104, and thereafter an ashing step for removing the resist 105 is performed. In the ashing step, an ashing damage may be exerted on the SiOCH-based film 102, and an oxide layer 106 may be formed on the side surfaces of the groove 105. This is considered to be because the material constituting the SiOCH-based film 102 itself is very instable, and oxidation thereof will easily proceed due to the presence of an excess of oxygen (O) radicals and the like. It has been reported that, when a wet treatment is conducted as an after-treatment under the condition where the ashing damage is exerted, as shown in FIG. 6B, the oxide layer 106 is cut, to generate unrequited size conversion differences, steps at the side walls of the groove 105 or the like, resulting in that a Cu wiring (omitted in the figure) embedded in the groove 105 cannot have the desired characteristics.
In the above-mentioned ashing step, therefore, it is demanded to establish a technique of suppressing the ashing damage while removing the resist pattern composed of an organic material. For this purpose, it is necessary to accurately monitor the amount of the oxygen (O) radicals during the ashing step.
Conventionally, the actinometric method has been applied to the monitoring of the O radical amount. The actinometric method is a method in which the absolute value of the O radical amount is determined from the ratio between the luminous intensity of oxygen and the luminous intensity of argon (Ar), which is introduced together with oxygen (see “Plasma Source Sci. Technol.”, (England), 1994, Vol. 3, pp. 154-161).
In the above-mentioned actinometric method, however, it has been impossible to accurately monitor the O radical amount. FIG. 7 shows a graph in which the amount of oxygen radicals determined by the actinometric method is taken on the axis of abscissas, and the ashing rate of the resist is taken on the axis of ordinates. Here, the ashing rate of the resist is expected to be proportional to the O radical amount. However, the O radical concentration actually determined by the actinometric method is not proportional to the ashing rate; thus, it is seen that accurate monitoring of the O radical concentration is not achieved.
This is because, on one hand, the luminous intensity of oxygen (wavelength λ=777 nm) ordinarily measured includes not only the luminescence of the O atomic radicals but also the dissociational luminescence of oxygen molecules (O2), but, on the other hand, in the actinometric method the O radical concentration is determined by regarding the luminous intensity at the wavelength λ=777 nm measured as the luminescence relevant only to the O radicals.